Suspended ceiling systems are well-known in which a plurality of main runners extend parallel to each other, with cross members extending between the main runner at spaced intervals for supporting ceiling tiles or panels. The main runners and cross members, or cross tees, generally have an inverted T cross-sectional configuration, with a pair of oppositely-extending flanges connected by a web portion to a reinforcing bulb or bead. The cross members are typically connected to the main runners by a tongue that extends from the ends of the cross members and are received in an elongated slot in the web of the main runner.
It is also known to provide for a “fire rated” suspended ceiling system in which the connection between the main runners and the associated cross tees allows for limited expansion of the cross tees caused by an elevated temperature that would result from a fire without buckling the main runners. See, e.g., U.S. Pat. Nos. 4,601,153 and 4,677,802, both of which are incorporated herein by reference.
More recently, ceiling grid systems have been developed that allow for lateral movement of the cross members both into and away from the main runners, while maintaining the assembled relationship of the grid system, for use in geographical regions subject to earthquakes. Standards and requirements have been promulgated for ceiling suspension systems and areas requiring seismic restraint. Specifically, the International Building Code (“IBC”) requires the provision of a seismic separation joint for all ceiling areas exceeding 2,500 square feet. One method for providing for the separation joint is disclosed in U.S. Published Application US 2007/0180787, where joint clips are provided which attach to the grid at the points of intersection of the main runners and the cross-members. The clips support the reinforcing bulbs of the grid member so that the cross tees continue to be supported by the main runners upon separation. Consequently, an over-wide flange on the main runners is not required for support of the cross members.
By way of the present disclosure, an improved separation joint is provided. Specifically, the present disclosure provides for a seismic separation joint that does not require an additional clip member.